Rugged vacuum tube



HL H. PORTER ETAL 2 Sheets-Sheet 1 Filed Jan. 24, 1944 FIG. 6

NVENTORS HENRY H. PORTER SEBASTIAN KRRER BY RAYMOND D. N/NDL/N JAMES A. VA/VLLEN ATTORNEY Dec. 3, 1963 H. H. PORTER ETAL 3,113,235

RUGGED VACUUM TUBE` Filed Jan. 24, 1944 2 Sheets-Sheet 2 Angling! United States Patent C) 3,lll3,235 RUGSED VACUUM TUBE Henry H. Porter, Silver Spring, Md., Sebastian Kar-rer, Washington, D52., Raymond D. Nindlin, New York, NX., and laines A. Van Alien, Silver Spring, Md., assignors to the United States of America as represented by the Secretary of the Navy llhled Eau. 24, walt, Ser. No. ih'i 2 Claims. (Cl. 313-285) This invention relates to electrical space discharge devices and has particular reference to a novel vacuum tube characterized by its rugged construction. The new vacuum tube may be made in `a compact form and is `capable of withstanding high stresses in at least one direction, and, therefore, is admirably suited for use 4in `devices which are subjected to heavy shock, such as projectiles which are propelled with a high acceleration. Accordingly, the invention will be described in connection with a so-called proximity fuze for projectiles adapted to be fired from a gun, although it will be understood that the invention may be used for other purposes as well.

Vacuum tubes of extremely rugged construction are required in certain types of proximity fuzes, such as that disclosed in a copending application of M. A. Tuve et al., Serial No. 471,388, tiled January 6, 1943. It has been established by tests that vacuum tubes as manufactured heretofore are not sufficiently rugged in construction to withstand the stresses created within a rotating projectile at the time of its acceleration in a gun barrel and during its iiight toward a target. While vacuum tubes have been devised in which a greater degree of ruggedness is obtained than in the conventional type, these tubes were not developed with a view to withstanding the stresses encountered in projectiles and are not sufiicicntly rugged for such use.

We have 4found that the problem of obtaining ruggedness in vacuum tubes is not capable of solution merely by improving the construction of certain components of the tube. On the contrary, we have kfound that many factors contribute to the success of a vacuum tube which is suiiiciently rugged to withstand stresses of the order encountered in projectiles. More specifically, all of the components of a rugged vacuum tube should be of such size, shape and -construction that they will, when properly assembled into a unit, cooperate to withstand setback, centrifugal and other forces exerted in a projectile when it is fired.

One object of the present invention, therefore, resides in the provision of a novel electrical space discharge vacuum tube which is operable under heavy stresses, such as the large forces of acceleration present in a projectile when it is fired from a gun.

Another object of the invention is to provide a rugged vacuum tube for use in rotary projectiles, which is adapted to withstand the large centrifugal forces encountered in such projectiles due to their high speed of rotation.

A further object of the invention is to provide an electrical space discharge vacuum tube of rugged construction and small size which may be readily assembled.

Still another object of the invention is to provide a vacuum tube having novel means for supporting the lilarnent cathode so that it is maintained in properly spaced relation to the associated electrode elements and is prevented `from sagging.

An additional object of the invention is to provide in an electrical space discharge vacuum tube a spring for supporting the upper end of the lament to maintain the iilament under the proper tension at all times.

These and other objects of the invention may be bet- CII llzi

Patented Dec. 3, i963 ICC ter understood by reference to the accompanying drawings, in which FIG. 1 is 4an enlarged perspective View of one form of the new vacuum tube, with parts of the envelope and the tube elements therein broken away to show the internal structure;

FIG. 2 is a detail perspective view of part. of the tube, showing the construction and mounting of the spring for supporting the upper end of the iilament and maintai-ning it under tension, and also showing the addition of a restrainer for limiting the filament against lateral vibration;

FiG. 3 is an enlarged side view oi a modied support structure for the upper end of the filament;

FIG. 4 is a detail perspective View of a further modiiication of the supporting structure for the upper end of the iilament;

FIG. 5 is a transverse sectional view of the tube illustrated in FiG. ll, with parts broken away, showing the upper mica support and its associated elements;

HG. 6 is aperspective View of part of the tube of FiG. l, showing the upper and lower mica supports;

FiG. 7 is a similar view showing how the plate elements are mounted on the supporting frames and how the trames are connected to the supporting yokes;

FIG. 8 is an enlarged perspective View of a modified form of the new vacuum tube, with parts of the envelope broken away to show the internal structure;

FIG. 9 is a transverse sectional -view on the line 9 9 in FlG. 8, and

FIG. l() is an exploded View of part of the internal structure shown in FIGS. 8 and 9.

Referring to the drawings, the vacuum tube comprises an envelope l() made of glass or other suitable material, the envelope, as shown, being elongated and substantially elliptical in cross-section, although it may be of any other desired shape. if an envelope of elliptical cross-section is employed, the supporting micas ll and i2, to be described in detail presently, are :also elliptical in shape so as to engage the side walls of the envelope and prevent torsional and lateral movement of the elements within the envelope. Alternatively, the inner structure may be constructed so as to be self-rigid without requiring support from the envelope. It should be noted lthat there is a definite cooperative relation between the envelope length, its circumference and the thickness and strength of its side wall. More particularly, in its preferred form the envelope is short and has a small perimeter and a side wall of sufficient thickness to afford great strength. it has been yfound that an envelope of this construction is capable of withstanding the stresses exerted in a rotating projectile during its acceleration and iiight, and its use is one of the factors contributing to the success of the rugged tube. While the envelope, and its contents, as shown, are many times larger than is necessary, it is apparent that the size may be varied to suit particular conditions, although the proper ratio between the envelope length, wall thickness, and circumference should be maintained.

The envelope is closed at its lower end Where it `is formed with a press NA Afor supporting the electrode elements. A plurality of wires 13 to 2i, inclusive, are embedded in the press MBA and project into the envelope, the wires being of sufiicient size to provide a rigid support for the electrode assembly, the elements of which will be described in detail presently.

If the upper part of the electrode structure is not supported against the envelope, the lead wires preferably are not aligned in a straight line in the press, or header, but are placed at the corners of a triangle, quadrilateral, pentagon, etc.

The upper ends of the wires l5 and 19 are welded to yokes `22 and 23, respectively, which are made of thin sheet metal and serve to support the anode or plate of the electrode assembly. The yolres, as best shown in FIGS. 1 and 7, are generally U-shaped in front elevation, and each yoke has partially bowed and rolled side edges 24 and 25, and a bowed central portion 26 which receives the upper end portion of the corresponding wire l or 19 and provides a rigid mounting for the yoke. Mounted on the yokes 22 and 23 are inverted U-shaped plate-supporting vframes 27 and 2S, each having legs 29 and 3d and bight portions 31. The lower end portions of the legs 2i? and 39 of frame 27 project through the lower mica 1l and are anchored in the rolled edge portions 24.- of the yokes 22 and 23, while the lower end portions of the legs of the other frame 28 project through the mica l1 and are anchored in the rolled edges 25 of the yokes. The legs 29 and 3ft also project through and support the upper mica 12, the micas 1l and 12 serving to retain the electrode assembly in properly spaced relation to the wall of the envelope 10. The micas are mounted in the envelope with their edges `in tight frictional engagement with the side walls of the envelope to prevent displacement of the micas. lf desired, the envelope may be formed with inwardly extending detents 32 for retaining the micas against displacement in the event that their edges do not have suficient `frictional engagement with the side Walls of the envelope.

Between the micas 1i and 12 are plate elements 34 and 3S which extend between the legs of the frames 27 and 23, respectively, and cooperate to define the anode or plate 36 of the electrode assembly. The side edges of the plate elements 3d` and 35 are partially rolled about the legs of the frames 27 and 26, as shown yat 34A and 35A, and are welded to the legs so that the plate elements are rigidly mounted. ySince the lower ends of the legs 29 and 3i) of each frame are mounted in the adjacent side portions of the yokes 22 and 23, We provide a rigid support for the frames `27 and 2S and for the plate 36.

A getter 37, which may take any desired form, is fixed to the upper end of a supporting post 38 welded at its lower end to the wire 21. The lsupporting post 38 is of suficient strength to provide lthe necessary vsupport for the getter assembly and for one end of a suppresser grid 39.

The post 38 extends through the micas lll and 12 and partly supports the suppresser grid 39 which, as shown, is in the form of a thin wire coiled around Ia frame provided by the post 3S and a filament-supporting post 4G near opposite sides of the envelope. The lower end of post 4d is Welded to the upper end of wire 13. The post d, like the post 38, extends `through the micas 11 and 12 and projects above the mica 12, the two posts being disposed near the ends of the micas and medially of their widths, as shown in FIGS. 1 and 6. Secured to the post 40 on the upper face of mica 12 is a horizontally extending anchoring bar 431., and on the upper end portion of post 4t) above bar 41 is a crossbar d2. The bars 41 and 42 extend horizontally from each side of post d@ and provide a mounting for the resilient filament support to be described presently.

A lament or cathode 43, which may be made of tungstenor other suitable material, extends through the micas 11 and 1l2 substanitally axially of the envelope. As shown in FiGS. 1 and 6, the lower end of the filament is Welded to a tab 44 secured to a strip l5 which forms part of a filament mounting unit including supporting posts or stakes 47 secured at their upper ends to the mica 1l. The unit `i5-47 is rigidly mounted in position on the wire 17 which is welded to the lower end of a stem 17A, the upper end of which is welded to the strip 45.

:Before describing the Support for the upper end of the filament or cathode 43 (PEG. 6), it is desired to state that computations and experiments have established that certain criteria should be satisfied by a mechanism for supporting the upper end of the filament under proper tension. IMore particularly, it has been determined that the filament tension should be unusually high for the following reasons:

(a) A filament (or string), when rotating about an axis approximately parallel to the axis of the filament, becomes unstable laterally when the angular velocity of rotation exceeds a certain value which is proportional to the square root of the tension. If this criterion of lateral stability is exceeded, the filament undergoes a large transverse bowing which results in one or more of the following adverse conditions, all of which are intolerable:

(1) A change in electrical characteristics of the electronic device.

(2) An electrical short circuit with adjacent electrodes.

(3) Microphonic disturbances.

(4) lFracture of the filament.

(5) Chipping ofi of the filament coating.

(b) The greater the eccentricity of the axis of the filament with respect to the axis of rotation of a projectile containing the tube, the higher the filament tension must be in order to prevent excessive bowing of the filament due to the action of the intense transverse field of centripetal acceleration, which may reach a magnitude of `the order of 10,00() times the acceleration of gravity.

,(c) lf the axis of the filament is transverse to the axis of rotation, excessive bowing results from the acceleration parallel to the axis of the projectil unless the filament tension is sufficiently high.

(d) .lvlicrophonic disturbances of low frequencies are undesirable in vacuum tubes of the type described. lnastnuch as the frequency of vibration of the tilarnent increases with the filament tension, a high tension is reu quired.

(e) Microphonic disturbances of large amplitudes are undesirable in vacuum tubes of the type described. Since the amplitude of microphonic disturbances decreases as the filament bowing decreases, and since the filament bowing' decreases as the filament tension increases, a high tension is desirable.

lt has also been determined that the deflection of a filament-supporting spring must be large in order to produce the required tension, for the following reasons:

(a) Due to the thermal expansion of the filament when heated to perform its function of emiting electrons, the length of the filament is increased and the tension in the filament, accordingly, is reduced in the ratio of the change of filament length to the deiiection of the spring required to produce the initial filament tension. This is -so because the tension in the filament is approximately proportional to the deiiection of the spring. Therefore, in order to retain a large proportion of the filament tension, the deflection of the spring must be large in comparison with the thermal elongation of the filament.

(b) In order to obtain uniformity of filament tension in large numbers of hand-assembled devices, the spring deflection must be large in comparison `with errors in the specified deflection which are introduced -unavoidably by the assembler. The variation in tension is proportional to the ratio of error in deflection to total deflection.

The stress in the spring should be small for the following reasons:

(a) If the spring is defiected to such an extent that the maximum fiber stress exceeds the yield point of the spring material, the tension applied to the iiiament is not proportional to the deliection of the spring, and little additional tension is obtained by deflecting the spring beyond its yield point.

(b) Part of the processing of our vacuum tubes in volves heating the components in the tube to high tem-- peratures in order to drive off undesired gases before or during evacuation, or both. As the temperature increases, the rate of increase of the spring stress with respect to the deflection decreases very rapidly, While the rel-ationl between stress in the spring and the filament tension remains practically unchanged. Therefore, when a highly stressed `spring is heated during processing, it takes on a permanent set in its defiected position and most of the filament tension is lost. The lower the initial stress in the spring, the less will be the proportion of `filament tension lost during heating. Accordingly, it is desirable to rnploy a spring in which the required filament tension is obtained with a spring fiber stress which is small in comparison with its yield point at the elevated temperatures.

An additional criterion for the filament-supporting structure is that the spring be relatively small even though the required filament tension is usually high. Also, the spring should be of such design that it may be readily manufactured and installed, in order that the vacuum tubes of our invention may be made in large quantities. Moreover, even though the spring exerts an unusually high tension on the filament, any additional tension exerted by the spring on the filament during the acceleration and flight of the projectile should be small. These additional criteria are based upon the following considerations:

(a) If the relative positions of the spring and filament are such that any part of the mass of the spring, multiplied by the acceleration of the projectile, is equivalent to a force added to the tension of the filament, then the mass of the spring should be small in order that the added force be insufficient to break the filament.

(b) if, on the other hand, the relative positions of the Spring and filament are such that the filament tension is relieved by additional spring deflection during acceleration, then the product of the additional deflection, the mass ofthe deflected portion, and its acceleration (energy) must not be so great as to exceed the maximum strain energy that can be absorbed in the filament before it breaks. For a given acceleration, this can be done either by reducing the mass of the spring or by limiting its additional defiection by means of a stop.

rl`he support for the upper ends of the filament (FIG. 6) is shown generally at 4S and may be referred to as a helical hook. The helical hook is made of resilient wire and includes a spring 49 coiled around the crossbar d2 and preferably pre-formed on a suitable mandrel, although the spring may, if desired, by wound around the crossbar 4Z. One end of the spring 49 projects downwardly and has its lower end secured to the anchoring bar di, while the other end of the spring, in the form of an arm Sil, projects obliquely upwardly above the mica l2. A tab Si is welded to the outer end of the arm 5t?, and the upper end of the iiiament 43 is welded to the tab. The size and weight of the tab are carefully predetermined so that its inertial force does not contribute materially to the tension exerted on the filament during acceleration of the vacuum tube in a projectile, whereby filament breakage is prevented or substantially reduced.

The upper end portion of the filament 43 projects through the crotch of a ear-shaped opening S3 in the upper mica 12, from which the filament extends obliquely upwardly to the tab 5l. It should be noted that the tension in the spring 43 acting throught the arm d@ exerts enough upward pull on the filament to maintain it normally under such tension that the frequencies of any filament microphonics which might occur are well above the audio-frequencies at which the tube is to operate. As previously stated, however, the tension exerted by the spring 43 on the filament is not so great that filament breakage will occur. To insure that the filament is placed under proper tension during manufacture of the electrode assembly, the arm 5b is swung down against the tension of spring tti through an angle of substantially 90 degrees to the position shown in FIG. 6, after which the filament is attached. Since the arm Sti forms a part of the spring d8 and, therefore, is not connected directly to bar d2, damping of lateral oscillations of the arm 50 will be effected by engagement of the coils of the spring 48 with the bar 42, with the result that filament breakage due to side thrust is largely avoided.

The electrode assembly includes a screen grid 54 which, as shown, is made of a thin wire coiled around a pair of supporting posts 55 and 56 within the suppressor grid 39, the posts 5'5 and 56 being secured to the upper ends of the wires M and 2f), respectively, by welding or in any other suitable manner. Also included. in the electrode assembly is a control grid 57 in the form of a thin wire coiled around supporting posts 58 and 4;-9 within the screen grid 54. The posts 58 and 59 are welded or otherwise secured to the upper ends of the wires 16 and J18, respectively. All of the grids of the electrode assembly are made of wire of sufficient strength to withstand the stresses exerted by the setback and centrifugal forces encountered in the projectile.

rThe electrical operation of our rugged vacuum tube is conventional and, therefore, a detailed description of the operation is unnecessary. While the tube as illustrated is of the pentode type, it will be apparent that our new construction may be employed in triodes or tubes having other arrangements of the electrode elements, without departing from the scope of the invention. Also the structural features contributing to the ruggedness of our tube may be modified to suit different conditions.

Referring now to FIG. 2, We have shown a modified fiiament-supporting structure similar to that shown in FIGS. l and 6 except for the addition of a restrainer 60 on the bar i2 for limiting lateral movement of the outer end portion of spring arm 5ft. The restrainer includes an obliquely depending arm 6l bearing against the spring arm 5t) to retard lateral oscillation thereof.. The shape of the restrainer may, if desired, be varied to suit particular conditions.

In the modifications shown in FIG. 3, a slightly different supporting structure for the upper end of the filament is employed. The filament 43 has its upper end secured to a tab 62 welded to the outer end of a cantilever spring 63, the inner end of the spring 63 being connected directly to the upper end portion of the post di). The spring 63 is of such diameter and length that the filament is maintained under proper tension, with the result that filament breakages and microphonics are reduced or eliminated.

An additional criterion for a satisfactory filament-supporting member is that the spring be rigid in a plane transverse to the axis of the filament. A structure satisfying this criterion is illustrated in FIG. 4, which shows a double helical hook dit referred to as a mouse trap spring. The spring should be rigid in a plane transverse fito the axis of the filament for the following reasons:

(a) If the spring 64 is not sufficiently rigid in a plane transverse to the filament 43, the natural frequency of vibration of the spring in this piane is low, and jarring of the vacuum tube, as in firing a projectile containing the tube, sets up low-frequency vibrations in the spring which are transmitted to the filament, causing undesirable lowfrequency microphonics.

(b) The less rigid the spring 64 is in a plane transverse to the filament, the larger are the amplitudes of the transverse vibrations due to jarring, and the larger is the magnitude of the resulting undesirable filament microphonics.

(c) Defiection of the spring 64 in a direction transverse to the axis of the filament @t3 causes excessive bending of the filament where it joins the spring, if a nearby portion of the filament is held fixed, as by the mica spacer l2. The maximum stress in the fiiament is proportional to the tension therein and also to the filament curvature. Since our filament should have a high tension, for the reasons outlined above, it is important that the curvature of the filament, due to transverse displacement of the spring, be very small. if a portion of the filament near the spring is not secured `against lateral movement, there will be little bending of the filament at the spring, but if the spring is not rigid transversely, the filament will be `displaced with respect to the other electrodes, resulting in undesirable microphonics and changes in electrical characteristics.

ln FIG. 4, the numeral 65 indicates a supporting rod secured at its ends to posts 66 and 67 which are mounted on and project above the upper face of the mica l2. The spring 6d has coils 66 and 69 wound around the opposite end portions of rod 65, and intermediate its ends the spring has arms 70 and '7l which project outwardly from the rod 65 above the upper mica l2, the arms being joined in a bight 72. A tab 73 is welded to the bight, and the upper end of filament 43 is welded to the tab. The tab 72 is so positioned that the coiled portions 63 and 69 of the spring exert equal tensions on the arms 75l and 7i. The supporting rod 65 cooperates with the spring arms to define a closed loop of substantially triangular shape, so that lateral movement of the upper end of the filament, with probable breakage thereof, is prevented. It should be understood that the coiled spring portions 68 and 69 may be disposed on either side of the arms 76 and 7l. lt has been found, however, that the construction shown in FIG. 4 is easier to manufacture. The free ends of the coiled spring portions 63 and 69 may be welded or otherwise connected to an anchoring bar 7d similar to the bar lll.

The vacuum tube in the form illustrated is mounted in the projectile with the tip or seal of the tube toward the base of the projectile. However, the end of the filament i3 nearest the press 116A is designated as the bottom of the filament, while the end of the filament adjacent the tip or Seal is referred to as the top of the filament. lf the tension spring (48, 63 or 64) is mounted at the top of the filament, the tension in the filament is increased during linear acceleration of the projectile. Conversely, if the spring is disposed at the bottom ofthe filament d3, the tension is relaxed during linear acceleration of the projectile. Since it is desirable to maintain the filament tension within predetermined safe limits, the Weight of the spring and connecting tab (l, 62. or 72) is carefully predetermined. It has been found that if the spring and tab are of relatively light weight, filament breakage is greatly reduced. In other Words, the spring normally maintains the filament under a predetermined tension, and when the tube is subjected to acceleration, the mass of the tab and the arm (or arms) of the spring contributes its inertial force to the tension. We have also found that the filament tension should be such that the natural period of vibration of the filament is above the audio-frequencies to which the tube is to be operated,

As stated heretofore, it has been found that ordinary Vacuum tubes will not withstand 'the forces set up in a rotating projectile during its acceleration and flight. By way of example, these forces in a six-pounder gun firing at full charge are approximately as follows: Angular acceleration, up to 140,000 revolutions per second per second; linear acceleration, up to 20,000,000 centimeters per second per second; centripetal acceleration due to spin, up to 10,000,000 centimeters per second per second per centimeter radius. Vacuum tubes made in accordance with our invention have operated successfully under these large forces.

The new vacuum tube make be made in a compact form so that it occupies only a small amount of space, and tubes having an over-all envelope length of about 11/2" and a major diameter of 3s"are in successful operation in projectiles.

Tungsten has been found to be highly satisfactory for use in manufacturing the filament of the new vacuum tube, because by the use of this material high enough tensile stresses may be applied so that microphonic response within the operating frequencies of the tube is maintained at a minimum. The strength of other common materials suitable for use in the manufacture of lilaments (such as nickel) has been found insufficient to withstand the tension necessary to maintain the frequencies of the `microphonics above the operating frequencies.

I For the construction of thek grid windings, we have combined the unsupported length of whe, the overhand, the wire diameter and the density of the material in such a manner that the maximum stresses resulting from the acceleration do not exceed the strength of the material, .and so that the maximum deflections are not excessive. lt is necessary to maintain the maximum relative deflections of the electrodes small enough so that the electrical characteristics of the tube are essentially the same during flight of the projectile as before the flight.

The grid side rods 38, d6, 5S, 56, 56 and 59 are similarly designed and the combination of their unsupported length, diameter, density of material and mass of windings is such that the maximum stresses in the side rods do not exceed their strengths, and such that the maximum deiections are small when subjected to the accelerations encounted dur- Y .ing their use in a projectile,

Referring again to that form of our tube in which the inner structure is not rigidly supported laterally against the envelope, it was stated that the inner structure must, in this case, be made self-rigid. This is accomplished by introducing two features in combination. The first, already mentioned, is the arrangement of at least three lead wires in locations in the press, or header, not in a straight line. The second is the rigid interconnection of at least three of these lead wires at intervals along their lengths. When this combination is introduced, transverse deiiections of the structure are greatly reduced, since the forces tending to produce such deflections are resisted by direct tension and compression of the lead wires rather than by their flexure. ln addition, the vibration frequency of the structure is considerably increased by this construction.

In FlGS. 8, 9 and 10, we have illustrated one embodiment of the invention wherein the inner structure is not rigidly supported laterally against the envelope. As there shown, the tube comprises an envelope 76 made of glass or other suitable material and having dimensions and Wall thickness such as to afford great strength. The envelope 76 is closed at its lower end where it is formed with a press 76a for supporting the electrode elements. As illustrated, the envelope 76 is circular in cross-section, and the press 76a is generally cross shaped in cross-section. Within the envelope 76 are two spaced micas 77 and 78 of circular form which nt closely in the envelope. The micas are supported by four lead wires or rods 79, one of the rods being secured in each arm of the press 76a, whereby the rods and micas form a generally box-shaped frame. lt will be undestood that rods of any other desired number, not less than three, may be employed to provide a frame having the general shape of a triangle, a pentagon, etc.

The rods 79 project upwardly from the press into the `envelope 76 and are provided near their lower ends with enlargements 7% for supporting the lower mica 77. The micas 77 and 76 are spaced by a generally cylindrical plate element Sti having longitudinal, external grooves 80a for receiving the rods 79, whereby the plate Si) is held securely in position and contributes to the interconnection between the rods. The plate 36 is seated on the lower mica 77, and the upper end of the plate engages and supports the upper mica 78. At their upper ends, the rods 79 project through the upper mica 78, and the sleeves of a yoke til are mounted on the projecting ends of adjacent rods to further interconnect the rods and to secure the upper mica 73 agains t'ne plate 79. Additional sleeves 82 are mounted on the projecting upper ends of the other rods 79 to hold the mica 7S against the plate Sil. It will be apparent that the micas 77 and 765 serve as rigid interconnections between the supporting rods 79 at spaced intervals along their lengths.

A pair of supporting rods 34 and 85 extend longitudinally within the plate 3@ in spaced relation thereto and are mounted at their ends in the supporting micas 77 and 78 near diametrically opposite edges thereof. The rods 84 and 85 may be welded or otherwise secured to the micas. Mounted on the rods 84 and 85 is a suppressor grid 86 in the form of a thin wire coiled around the rods, as shown in FIG. 9. Within the suppressor grid coil 86 is a pair of rods 87 and 88 mounted on the micas and supporting a screen grid 89 in the form of a thin wire coiled around the rods 87 and 88. Similarly, another pair of rods 90 and 91 is mounted within the screen grid coil 89, the ends of the rods 90 and 91 being secured to the micas 77 and 7S. The rods 90 and 91 support a control grid 92 in the form of a thin wire coiled around these rods within the screen and suppressor grids. The supporting rods 84, 85, 87, 88, 91 and 92 are disposed in a common plane between the micas and are parallel to the lead wires 79.

A bracket 93 is mounted on top of the upper mica 78 and is welded or otherwise secured to the projecting end of rod 84. The bracket 93 supports at its upper end a cross arm 94 which, in turn, supports a tension spring 9S. The spring 95 includes coils 96 and 97 Wound around the opposite end portions of arm 94, and intermediate its ends the spring has converging arms which project outwardly from the cross arm 94 and are joined in a bight having a tab 98. The upper end of the tilarnent 99 is welded or otherwise secured to the bight 98, the ilament extending through a triangular opening 100 in mica 78, in the manner of the filament 43 illustrated in FIG. 3. The filament 99 extends through the control grid 92 and is suitably anchored at its lower end. The grids and filament are electrically connected to suitable wires 101 in the press 76a, and the wires 101, together with the lead wires 79, serve to connect the tube in circuit.

With this construction, the electrode elements have substantially straight-line support. That is, the supports for the elements are disposed in longitudinal, parallel relation so that when the tube is accelerated in a longitudinal direction, the supports are subjected to compressional forces rather than to bending forces, whereby the tube is better adapted to withstand such accelerations of a high magnitude.

In our tube, the length of lead wire sealed in the glass press, or header, is made suiciently `long so that the contact area between the metal lead and the glass is large enough to reduce, to a small enough value, the bond stress resulting from the pull of the lead during acceleration and spin.

The glass surrounding the lead wires is also shaped so as to reduce local stress concentrations in the glass which might result from the unusually large forces on the lead wires.

Referring again to the filament tensioning means, it will be noted that if a large spring deflection is to be obtained with a small spring stress, a long spring length is required. However, a long spring has a large mass and occupies a large space. Also, with a high filament tension, a long spring has a high spring stress. In the new tube we provide a long spring which occupies a small space, by winding most of the spring in the form of a compact coil or coils. This construction, together with the short cantilever portion of the spring, affords a large deflection and large load with a small stress. By supporting the coil of the lament tensioning spring on a xed stud, the spring includes only a small free mass which may be acted upon by setback when the projectile -is ired. It should be noted that we have obtained the desired large detlection of the filament tensioning spring by using the phenomenon of ilexure. However, in order to obtain transverse rigidity, it is necessary to eliminate flexure in the transverse direction. This is accomplished by making the spring symmetrical about a vertical plane 1n such a manner that the portion of the spr-ing on either side of the plane of symmetry acts as a brace for the portion on the other side.

We claim:

1. In a vacuum tube, an envelope having opposed flat walls and a press, wires in the press and extending into the envelope in planes parallel to the llat walls, a pair of flat yokes mounted in the envelope perpendicular to the at walls and in face-to-face parallel spaced relation to each other, a pair of anode elements in the envelope in parallel spaced relation to each other and perpendicular to said yokes, said yokes being supported by said wires, an inverted U-shaped frame supporting one of the anode elements with the legs or said frame having lower end portions connected to corresponding sides of the yokes, and a second inverted U-shaped frame supporting the other of the anode elements with the lower end portions of the legs of said second frame connected to conresponding yopposite sides of the yokes.

2.. In a vacuum tube, an envelope having opposed flat walls and a press, wires in the press and extending into the `envelope in planes parallel to the ilat walls, a pair of flat yokes mounted in the envelope perpendicular to the ilat walls and in face-to-face parallel spaced relation to each other, a pair of anode elements in the envelope in parallel spaced relation to each other and perpendicular to said yokes, said yokes being supported by said wires, an inverted U-shaped lframe supporting one of the anode elements with the legs of said frame having lower end portions connected to corresponding sides of the yokes, a second inverted U-shaped Vframe supporting the other of the anode elements with the lower end portions of the legs of said second frame connected to corresponding opposite sides of the yokes, and a pair of spaced transverse members in the envelope engaging the at walls thereof and bracing the legs of the frames, one transverse member being disposed near the bight portions of the frames and the other transverse member being dispo-sed near the end portions of said legs.

References Cited in the file of this patent UNITED STATES PATENTS 11,566,293 Van der Bijl Dec. 22, 1925 1,839,872 Freeman et al. Ian. 5, 1932 1,963,008 Weeks June 12, 1935 2,266,080 Rockwood Dec. 16, 1941 2,274,554 Krim Feb. 22, '1942 2,350,003 West May 30, 1944 2,355,083 Krim Aug. 8, 1944 2,402,797 Wood June 25, 1946 2,412,800 Curtis Dec. 17, 1946 

1. IN A VACUUM TUBE, AN ENVELOPE HAVING OPPOSED FLAT WALLS AND A PRESS, WIRES IN THE PRESS AND EXTENDING INTO THE ENVELOPE IN PLANES PARALLEL TO THE FLAT WALLS, A PAIR OF FLAT YOKES MOUNTED IN THE ENVELOPE PERPENDICULAR TO THE FLAT WALLS AND IN FACE-TO-FACE PARALLEL SPACED RELATION TO EACH OTHER, A PAIR OF ANODE ELEMENTS IN THE ENVELOPE IN PARALLEL SPACED RELATION TO EACH OTHER AND PERPENDICULAR TO SAID YOKES, SAID YOKES BEING SUPPORTED BY SAID WIRES, 